Rotary shredders are well known apparatus which are used in a variety of situations so as to comminute waste material (e.g., tires, glass, masonry, wood and the like) for purposes of reducing the bulk of such waste material and/or to more easily facilitate recycling. In general, conventional rotary shredding apparatus are provided with a pair of parallel, horizontally spaced-apart, driven cutter shafts each of which mounts a series of alternating disc-type cutter and spacer elements equally spaced-apart along the shaft axes. The cutter discs on the shafts are interdigitated. That is, the cutter discs on one of the shafts are thus fixed at a position along the shaft axis so that they extend into the space between the cutters on the other shaft--i.e., into the spaces between the cutter discs established by the spacer discs.
The cutter shafts are counter-rotated so that the upper portions of the cutter discs on the two shafts rotate toward each other to force material fed into the apparatus from above downwardly between the two shafts where the material is shredded in the nip between the interdigitated cutter and spacer elements. (See, for example, U.S. Pat. No. 4,034,918, the entire content of which is incorporated expressly hereinto by reference.)
Conventional rotary shredders are typically provided with a plurality of immovable finger elements which extend inwardly toward the cutter/spacer discs. The purpose of such finger elements is to strip shredded material from the cutter and spacer discs to thereby prevent such shredded material from wrapping around the cutter shafts and overloading the shaft drives. However, practice has shown that for some fibrous waste material (e.g., waste carpet), immovably mounted finger elements do not serve their intended purpose.
In this regard, shredded waste fibrous material typically will overhang the tip of conventional cutter hooks. This overhanging material cannot be satisfactorily stripped from the cutters with traditional fingers and thus normally become jammed in between the fingers (known in art parlance as "bearding"). Severe bearding results in overload conditions in downstream processing equipment since material typically would build to a large mass within the shredder and then fall into the discharge chute. The mass of material can be so great as to sometimes jam or stall the conveying systems.
Traditional tight fitting fixed fingers of welded construction cannot be assembled to the necessary tight running clearances because of weld distortion and typical variations in the shredder body weldment. To maintain as tight a fit as possible, the shredder is typically used as an assembly jig. Once removed, these fingers are difficult or sometimes impossible to reassemble due to weld distortion and their custom fit within the shredder body.
It has now been discovered, however, that waste fibrous material may be satisfactorily stripped from the cutter and spacer discs if the finger elements are mounted to allow for slight, but meaning, movements relative to the cutter and spacer discs. That is, according to the present invention, the finger elements are not immovable, but instead are purposefully mounted relative to the cutter and spacer discs so that some movement is allowed during the shredding operation.
The moveable fingers according to the present invention thus permit shredder operation with tighter cutter-to-finger clearance than would be practical with conventional fixed-position (immovable) fibers. Side clearances may be held to tighter running fits because the finger can move and self-align. The finger section that is aligned with the knife hook is thus designed for tight clearance to the knife tip to "nip off" material that overhangs the knife hook. For materials such as fibers, it is especially desirable to make the knife and spacer discs an integral component to enable one to further reduce the knife tip-to-finger running clearance.
Preferably, according to the present invention, a series of individual finger blocks is mounted to the shredder frame to allow for selected ones of the individual finger blocks to be removed (e.g., for repair or replacement) without removal of the remaining finger blocks in the series. Each of the individual finger blocks preferably includes unitary cutter and spacer fingers extending generally radially towards the cutter and spacer discs, respectively. That is, the cutter and spacer finger discs extend generally radially toward a respective one of the cutter and spacer discs so as to strip shredded material therefrom.
The individual finger blocks of this invention provide improved serviceability. That is, (i) the finger blocks can be individually removed and replaced; (ii) the finger blocks can be premanufactured and assembled at the site with a controlled fit; (iii) only worn or damaged finger blocks need to be replaced; and (iv) individual finger blocks are light and easily handled.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiment thereof.